Treadmill test helps detect risk of cardiac arrest

A non-invasive treadmill test is allowing more South Floridians to avoid America's No. 1 killer — sudden cardiac arrest, a sneaky attacker that strikes without warning and kills 75 to 90 percent of its victims.

The Microvolt T-Wave Alternans screening gauges the strength of the heart's electrical output, arming doctors with better insight into whether a patient is at high risk for the electrical disturbance that causes sudden cardiac arrest. The test has been available at certain cardiologists' offices for years, but only in the past year or two has it received widespread acceptance by insurers for health care coverage.

The implications for survival of silent heart disease sufferers who otherwise would have escaped notice are enormous, area heart doctors say.

"I've seen it make a difference in a number of my patients," said Miami cardiologist Dr. Ralph Nader, who has long used the t-wave test in his private practice. "Something could be wrong with your heart, and [through other screenings] we don't find anything. You're flying under the radar."

The only real solution for SCA is prevention, though such efforts have long been — in the words of one Fort Lauderdale cardiologist — "imperfect."

"The way we protect people who we think are at risk of sudden cardiac arrest is imperfect. It's insensitive and non-specific," said Dr. Ahmed Osman, a Fort Lauderdale clinical cardiac electrophysiologist who has been offering the Microvolt T-Wave Alternans test to his patients for years. "It is a very nice, very useful test, in my opinion. It helps save lives."

Now, all patients admitted to Broward Health Medical Center in Fort Lauderdale for a heart attack are recommended to undergo a Microvolt T-Wave Alternans screening before going home to determine how susceptible their weakened heart is to SCA, said Osman, whom the hospital called instrumental in advocating for the technology.

"It's great because when it gives you a negative, it gives the patient assurance that their probability of having sudden cardiac arrest is very faint," said Dr. Adel Sidky, a cardiologist in Boynton Beach. "This test has very high predictive value."

Developed in the 1980s by scientists at the Massachusetts Institute of Technology, the screening was approved by the Food and Drug Administration for SCA risk assessment in 2002. But like with many treatments and procedures, it took years and a number of studies confirming the test's effectiveness before the insurance industry embraced it on a widescale basis.

"Unfortunately, no matter how good a test is, no matter how good medicine is, it just doesn't fly until it catches up with the insurance companies," said Dr. Ashok Sharma, a Plantation interventional cardiologist who started using the test eight or nine years ago. "If the insurance company doesn't pay, the patient doesn't want it."

Some patients who have had a prior heart attack or other cardiac event fall in what Miami's Nader called "the gray zone" on echocardiograms, which calculate how much blood the heart is pumping out, called the ejection fraction. Those with an ejection fraction of over 50 are determined at low risk of SCA, while patients scoring below 35 are judged at high risk and receive a defibrillator implant.

But those in the 35-50 soft middle may be harboring a higher risk than doctors suspect. Aside from t-wave testing, the only way to gauge that risk is to perform an invasive test that requires opening the patient up, which carries its own dangers, Nader said.

"Some patients are very clear-cut," Sharma said. "But there are others who are kind of healthy, borderline, sitting on the fence, and you're trying to weed out those who need [defibrillators] and those who don't."

For those patients, the Microvolt T-Wave Alternans test proves key in digging deeper to determine the strength of the heart's electrical signal. Multiple sensors placed on the patient while walking on a treadmill measure the signal's amplitude, and if it varies too much between normal and abnormal, the patient's risk of SCA is determined to be high.

At that point, the patient is often implanted with a defibrillator, which would immediately shock the heart into action in the event of an SCA and counteract the electrical storm that causes the heart to suddenly seize up due to an abnormal rhythm. Without a defibrillator implant, an SCA victim would require almost immediate intervention from a portable defibrillator, or the person could die within minutes.

Robert Robbins, of Miami, was one such patient. After a coronary angiogram raised red flags about his heart's irregular beat, he underwent t-wave testing, among other screenings, and he scored in the high-risk range. He now has a defibrillator implant.

"I had no idea. I had absolutely no discomfort. I could have been walking around, talking to you and keeled over, and it's over with," said Robbins, 69. "I am a very, very lucky guy. I say thank God we have the procedures we have today."